I had a similar situation. 4500 roll-on had a horrible half second lag and a jerky throttle both on and off were the biggest issues for me. Nels Byerdorf of 2 wheel dynoworks completely cured both problems. It wasn't one of those "I think it's better 'cuz I just spent a bunch of money so I'll try to convince myself that it was worth it" type of deals. The problems simply disappeared after his map was installed. According to the dyno chart I also picked up 4 or 5hp!
His dyno is built into a trailer but I don't know if he travels your direction or not. You might want to contact him anyway. It's possible he knows someone in your area who can work similar magic.